System and method for location assurance of a mobile device

ABSTRACT

A system and method for determining whether an estimated location of a wireless device includes one or more forged location measurements. A first estimated location of the wireless device using a first set of location measurements is determined, and a second estimated location of the wireless device using a second set of location measurements is determined. The first estimated location may be compared to the second estimated location. One of the determined locations may then be identified as having one or more forged location measurements if the comparison between the first estimated location and second estimated location is greater than a predetermined threshold. The second set of location measurements may be produced using a location technology different than the location technology used to produce the first set of location measurements.

RELATED APPLICATIONS

The instant application is related to and claims the priority benefit ofU.S. Provisional Application No. 61/347,225, entitled, “Handset-AssistedA-GPS Spoofer,” filed May 21, 2010, the entirety of which isincorporated herein by reference.

BACKGROUND

Radio communication systems generally provide two-way voice and datacommunication between remote locations. Examples of such systems arecellular and personal communication system (“PCS”) radio systems,trunked radio systems, dispatch radio networks, and global mobilepersonal communication systems (“GMPCS”) such as satellite-basedsystems. Communication in these systems is conducted according to apre-defined standard. Mobile devices or stations, also known ashandsets, portables or radiotelephones, conform to the system standardto communicate with one or more fixed base stations. It is important todetermine the location of such a device capable of radio communicationespecially in an emergency situation. In addition, in 2001 the UnitedStates Federal Communications Commission (“FCC”) required that cellularhandsets must be geographically locatable. This capability is desirablefor emergency systems such as Enhanced 911 (“E-911”). The FCC requiresstringent accuracy and availability performance objectives and demandsthat cellular handsets be locatable within 100 meters 67% of the timefor network based solutions and within 50 meters 67% of the time forhandset based solutions.

Current generations of radio communication generally possess limitedmobile device location determination capability. In one technique, theposition of the mobile device is determined by monitoring mobile devicetransmissions at several base stations. From time of arrival orcomparable measurements, the mobile device's position may be calculated.However, the precision of this technique may be limited and, at times,may be insufficient to meet FCC requirements. In another technique, amobile device may be equipped with a receiver suitable for use with aGlobal Navigation Satellite System (“GNSS”) such as, but not limited to,the Global Positioning System (“GPS”). GPS is a radio positioning systemproviding subscribers with highly accurate position, velocity, and time(“PVT”) information.

FIG. 1 is a schematic representation of a constellation 100 of GPSsatellites 101. With reference to FIG. 1, GPS may include aconstellation of GPS satellites 101 in non-geosynchronous orbits aroundthe earth. The GPS satellites 101 travel in six orbital planes 102 withfour of the GPS satellites 101 in each plane. Of course, a multitude ofon-orbit spare satellites may also exist. Each orbital plane has aninclination of 55 degrees relative to the equator. In addition, eachorbital plane has an altitude of approximately 20,200 km (10,900 miles).The time required to travel the entire orbit is just under 12 hours.Thus, at any given location on the surface of the earth with clear viewof the sky, at least five GPS satellites are generally visible at anygiven time.

With GPS, signals from the satellites arrive at a GPS receiver and areconventionally utilized to determine the position of the receiver. GPSposition determination is made based on the time of arrival (“TOA”) ofvarious satellite signals. Each of the orbiting GPS satellites 101broadcasts spread spectrum microwave signals encoded with satelliteephemeris information and other information that allows a position to becalculated by the receiver. Presently, two types of GPS measurementscorresponding to each correlator channel with a locked GPS satellitesignal are available for GPS receivers. The two carrier signals, L1 andL2, possess frequencies of 1.5754 GHz and 1.2276 GHz, or wavelengths of0.1903 m and 0.2442 m, respectively. The L1 frequency carries thenavigation data as well as the standard positioning code, while the L2frequency carries the P code and is used for precision positioning codefor military applications. The signals are modulated using bi-phaseshift keying techniques. The signals are broadcast at precisely knowntimes and at precisely known intervals and each signal is encoded withits precise transmission time. There is also an L2C signal beingtransmitted by several satellites. The LC2C signal is a second civilianfrequency transmitted by GPS satellites. L1 transmits the CoarseAcquisition (“C/A”) code. L2C transmits L2CM (civil-moderate) and L2CL(civil long) codes. These codes allow a device to differentiate betweensatellites that are all transmitting on the same frequency. The C/A codeis 1 milliseconds long, the L2CM is 20 milliseconds long and the L2CL is1.5 seconds long. The L2C codes provide a more robust cross-correlationperformance so that reception of weak GPS signals is less affected bysimultaneously received strong GPS signals. The civil navigation message(“CNAV”) is the broadcast model that can be transmitted on the L2C andprovides a more accurate and frequent message than the legacy navigationmessage.

GPS receivers measure and analyze signals from the satellites, andestimate the corresponding coordinates of the receiver position, as wellas the instantaneous receiver clock bias. GPS receivers may also measurethe velocity of the receiver. The quality of these estimates dependsupon the number and the geometry of satellites in view, measurementerror and residual biases. Residual biases generally include satelliteephemeris bias, satellite and receiver clock errors, and ionospheric andtropospheric delays. If receiver clocks were perfectly synchronized withthe satellite clocks, only three range measurements would be needed toallow a user to compute a three-dimensional position. This process isknown as multilateration. However, given the engineering difficultiesand the expense of providing a receiver clock whose time is exactlysynchronized, conventional systems generally account for the amount bywhich the receiver clock time differs from the satellite clock time whencomputing a receiver's position. This clock bias is determined bycomputing a measurement from a fourth satellite using a processor in thereceiver that correlates the ranges measured from each satellite. Thisprocess requires four or more satellites from which four or moremeasurements can be obtained to estimate four unknowns x, y, z, b. Theunknowns are latitude, longitude, altitude and receiver clock offset.The amount b, by which the processor has added or subtracted time, isthe instantaneous bias between the receiver clock and the satelliteclock. It is possible to calculate a location with only three satelliteswhen additional information is available. For example, if the altitudeof the handset or mobile device is well known, then an arbitrarysatellite measurement may be included that is centered at the center ofthe earth and possesses a range defined as the distance from the centerof the earth to the known altitude of the handset or mobile device. Thealtitude of the handset may be known from another sensor or frominformation from the cell location in the case where the handset is in acellular network.

Assisted-GPS (“A-GPS”) has gained significant popularity recently inlight of stringent time to first fix (“TTFF”), i.e., first positiondetermination and sensitivity, requirements of the FCC E-911regulations. In A-GPS, a communications network and associatedinfrastructure may be utilized to assist the mobile GPS receiver, eitheras a standalone device or integrated with a mobile station or device.The general concept of A-GPS is to establish a GPS reference network(and/or a wide-area D-GPS network or a wide area reference network(“WARN”)) including receivers with clear views of the sky that mayoperate continuously. This reference network may also be connected withthe cellular infrastructure, may continuously monitor the real-timeconstellation status, and may provide data for each satellite at aparticular epoch time. For example, the reference network may provideephemeris information, UTC model information, ionosphere modelinformation, and other broadcast information to the cellularinfrastructure. As one skilled in the art would recognize, the GPSreference receiver and its server (or position determining entity) maybe located at any surveyed location with an open view of the sky.Typical A-GPS information may include, but is not limited to, data fordetermining a GPS receiver's approximate position, time synchronizationmark, satellite ephemerides, various model information and satellitedopplers. Different A-GPS services may omit some of these parameters;however, another component of the supplied information is theidentification of the satellites for which a device or GPS receivershould search. From such assistance data, a mobile device may attempt tosearch for and acquire satellite signals for the satellites included inthe assistance data. If, however, satellites are included in theassistance data that are not measurable by the mobile device (e.g., thesatellite is no longer visible, etc.), then the mobile device may wastetime and considerable power attempting to acquire measurements for thesatellite.

Civilian GPS signals are vulnerable to attacks such as blocking, jammingand spoofing. The goal of such attacks generally is to prevent aposition lock (e.g., blocking and jamming) or to feed a receiver falseinformation so that the receiver computes an erroneous time or location(e.g., spoofing). GPS receivers are generally aware when blocking orjamming is occurring because the receivers encounter a loss of signal.Spoofing, however, is a surreptitious attack.

Civilian GPS signals are widely used by government and privateindustries for important applications, including, but not limited to,public safety services, navigation, geolocation, hiking, surveying,robotics, tracking, etc. Unfortunately, civilian GPS signals are notsecure. Since GPS signal strength, measured at the Earth's surface atabout −160 dBw (1×10⁻¹⁶ watts), is roughly equivalent to viewing a 25watt light bulb from a distance of 10,000 miles, GPS signals may beblocked by destroying or shielding a receiver's antenna and may bejammed by a signal of a similar frequency but greater strength. Asstated above, however, blocking and jamming are not the greatestsecurity risk. A more pernicious attack involves feeding the receiverfake or forged satellite signals so that the receiver believes it islocated somewhere in space and time that it is not. Spoofing may beaccomplished by utilizing a GPS satellite simulator. Such simulators areuncontrolled and widely available. To conduct the spoofing attack, anadversary may broadcast a forged satellite signal with a higher signalstrength than the true signal, and the GPS receiver believes that theforged signal is actually a true GPS signal. The receiver may thenproceed to calculate erroneous position or time information based onthis forged signal.

It is also possible for an unscrupulous user or intermediary to alterthe software in a wireless device to manipulate satellite measurementsthereby causing a location determining system to calculate an incorrectlocation. This method of spoofing is generally termed as locationspoofing. Generally, if satellite measurements are manipulated in awireless device randomly, it is likely that a resulting positioncalculation may fail because the position of the respective satellitesmay be too far away from the actual code phase indicated location;however, a skillful user may calculate required code phases resulting inthe calculation of a spoofed or false location by the locationdetermining system.

Generally, spoofing detection has focused on detecting false radiofrequency signals arriving at the GPS receiver front-end and/orauthenticating location results provided to a third party. There is,however, a need in the art regarding the detection of falsified orspoofed measurements being provided to the respective positioncalculation function (“PCF”) which may or may not be embedded in anexemplary location server (“LS”). An LS may generally be a node in awireless network providing GPS assistance data to an A-GPS capabledevice. The device may utilize the assistance data to lock ontosatellites much faster than if no assistance data were available and mayalso allow the device to lock onto weaker signals reducing TTFF andincreasing yield. In a handset-assisted mode, the LS may also determinethe location of the device using measurements from the device and/or therespective network. The LS may also require the device to provide trueand accurate measurements (rather than falsified measurements) todetermined an accurate location for the device. The integrity of theresulting location is important as it may be used by emergency servicesoperators, used to provide value-added services, etc.

Although embodiments of the present subject matter may not preventspoofing attacks, these embodiments may alert a wireless device userand/or an operator of a location determining system to such suspiciousactivity thereby decreasing the probability that a spoofing attacksucceeds. Further embodiments of the present subject matter may beimplemented easily and inexpensively by retrofitting existing GPSreceivers and exemplary location determining systems.

Accordingly, there is a need for a method and system for determiningfalsified satellite measurements and/or falsified locations of a mobiledevice that would overcome the deficiencies of the prior art. Therefore,an embodiment of the present subject matter provides a method fordetermining whether an estimated location of a wireless device includesone or more forged location measurements. The method may includedetermining a first estimated location of the wireless device using afirst set of location measurements and determining a second estimatedlocation of the wireless device using a second set of locationmeasurements. The first estimated location may then be compared to thesecond estimated location. If the comparison between the first estimatedlocation and second estimated location is greater than a predeterminedthreshold, then one of the determined locations may be identified ashaving one or more forged location measurements.

Another embodiment of the present subject matter provides a method fordetermining whether an estimated location of a wireless device includesa forged location measurement. The method may include determining afirst estimated location of the wireless device from information orsignals provided by a cellular network and determining a secondestimated location of the wireless device from signals received from aset of satellites. The first and second estimated locations may then becompared. If the comparison between the first estimated location andsecond estimated location is greater than a predetermined threshold,then the second estimated location may be identified as having one ormore forged signals.

A further embodiment of the present subject matter may provide a systemfor determining whether an estimated location of a wireless deviceincludes one or more forged location measurements. The system mayinclude circuitry for determining a first estimated location of thewireless device from a first set of location measurements and circuitryfor determining a second estimated location of the wireless device froma second set of location measurements. The system may also includecircuitry for comparing the first estimated location to the secondestimated location and circuitry for identifying one of the determinedlocations as having one or more forged location measurements if thecomparison between the first estimated location and second estimatedlocation is greater than a predetermined threshold.

These embodiments and many other objects and advantages thereof will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a constellation of GPSsatellites.

FIG. 2 is a representation of an exemplary A-GPS server in a wirelessnetwork.

FIG. 3 is a schematic representation of a SET falsifying its location tothe SLP of FIG. 2.

FIG. 4 is an illustration of a network-initiated, SET-assisted process.

FIG. 5 is an illustration of a SET-initiated, SET-assisted process.

FIG. 6 is a schematic representation of one embodiment of the presentsubject matter.

FIG. 7 is a schematic representation of another embodiment of thepresent subject matter.

FIG. 8 is a schematic representation of a further embodiment of thepresent subject matter.

FIG. 9 is a schematic representation of an additional embodiment of thepresent subject matter.

FIG. 10 is a block diagram of one embodiment of the present subjectmatter.

FIG. 11 is a block diagram of one embodiment of the present subjectmatter.

DETAILED DESCRIPTION

With reference to the figures where like elements have been given likenumerical designations to facilitate an understanding of the presentsubject matter, the various embodiments of a system and method forlocation assurance of a mobile device are herein described.

The present disclosure relates to a mobile appliance, handset or deviceand a location determining system using satellite signals and/ormeasurements of these satellite signals as well as location measurementsfrom other networks and location technologies. The satellites may beconsidered as part of a Global Navigation Satellite System (“GNSS”),such as, but not limited to, the U.S. Global Positioning System (“GPS”).While the following description references the GPS system, this in noway should be interpreted as limiting the scope of the claims appendedherewith. As is known to those of skill in the art, other GNSS systemsoperate, for the purposes of this disclosure, similarly to GPS, such as,but not limited to, the European Satellite project, Galileo; the Russiansatellite navigation system, GLONASS; the Japanese Quasi-ZenithSatellite System (“QZSS”), the Indian Regional Navigational SatelliteSystem (“IRNSS”), and the Chinese satellite navigation and positioningsystem called Beidou (or Compass). Therefore, references in thedisclosure to GPS and/or GNSS, where applicable, as known to those ofskill in the art, apply to the above-listed GNSS systems as well asother GNSS systems not listed above. Further, the terms spoofed,falsified, forged, and various tenses and forms thereof are utilizedinterchangeably throughout this disclosure and such use should in no wayshould be interpreted as limiting the scope of the claims appendedherewith.

As discussed above, A-GPS devices or handsets may have a low TTFF as thedevices are supplied with assistance data from an exemplarycommunications network to assist in locking onto or acquiring satellitesquickly. Exemplary A-GPS devices may include, but are not limited to, acellular device, text messaging device, computer, portable computer,vehicle locating device, vehicle security device, communication device,and wireless transceiver. These devices may provide satellitemeasurements back to a location determining system to perform a positioncalculation. Exemplary network elements that supply the assistance dataand/or perform the position calculation may be a location determiningsystem such as a Mobile Location Center (“MLC”), location informationserver or system (“LIS” or “LS”), or other comparable network element.The location determining system may generally be a node in a wirelessnetwork performing or determining the location of a mobile device. Thelocation determining system generally requires a wireless device toprovide true and accurate measurements (rather than forged measurements)to determine an accurate location of a device or provide accurateassistance data for the device. The integrity of the resulting locationis important as the location may be used by emergency services operatorsto find an injured person, may be used for location-based services, etc.

In one embodiment of the present subject matter, an exemplary method maybe utilized to determine whether a geographic location of a mobile orwireless device (or signals used therefor) has been spoofed or forged.One exemplary A-GPS server in a wireless network according to anembodiment of the present subject matter is shown in FIG. 2. Withreference to FIG. 2, an exemplary LS may be, but is not limited to, aSecure User Plane Location (SUPL) Location Platform (SLP) 210. Ofcourse, in a GSM network the LS may be a Serving Mobile Location Center(SMLC), a Standalone SMLC (SAS) in a UMTS network, or another type ofnetwork and/or node therein. The SLP 210 may generally be a networkentity facilitating the location determination of devices in thenetwork. A User Plane Location Protocol (ULP) (an HTTP-based protocol)may be, in one embodiment, employed between the SLP 210 and the wirelessdevice or a SUPL-Enabled Terminal (SET) 212.

An exemplary SLP 210 may be provided with a connection to a GNSSReference Server (GRS) 220 to retrieve and/or cache assistance data. TheGRS 220 may include a network of reference receivers 222, e.g., GNSSreceivers, and a central system adaptable to collate assistance datafrom any number of satellites 224 so assistance data may be availableupon request. The SLP 210 may also be provided with a connection to atime server using Network Time Protocol (NTP) 230 to maintain thecorrect time thereon. Location requests may be initiated either from theSET 212 (i.e., a SET-initiated transaction) or from the network (i.e., aNetwork-initiated transaction). In one embodiment, a Network-initiatedrequest may be provided by a Location Based Application (LBA) 240 to theSLP 210 for the location of a target SET 212. In a non-limitingembodiment, the LBA 240 may provide value added services such as afind-a-friend application, an emergency services application, or anotherlocation based services application. The SLP 210 may thus performapplicable messaging functions with the SET 212 and may determine alocation of the SET 212 before returning that location to the LBA 240.

In one embodiment, when an A-GPS location fix is required for a SET 212,the SLP 210 may determine GPS assistance data specific to an approximatelocation of the SET 212. For example, when the SET 212 is in a cellularnetwork 250, an approximate location may be provided by the coveragearea of the serving cell 252. Of course, the approximate location of theSET 212 may be provided by any number of means and such an exampleshould not limit the claims appended herewith. The SET 212 may thenprovide an identification of the serving cell 252 (e.g., Cell-ID) to theSLP 210, and the SLP 210 may determine which satellites 224 are in viewfrom the approximate location and provide applicable assistance data forthose satellites 224 to the SET 212. Exemplary assistance data may, inone embodiment, depend upon the mode of A-GPS. For example, in ahandset-based A-GPS embodiment, the SLP 210 may provide the navigationmodel, ionosphere model, reference time, and reference location wherebythe SET 212 utilizes this information to lock onto satellites 224 anddetermine its respective location. By way of a further example, in ahandset-assisted mode, the SLP 210 may provide acquisition assistanceand reference time to allow the SET 212 to lock onto satellites 224 andreturn the applicable measurements to the SLP 210. The SLP 210 may then,in one embodiment, invoke a PCF 214 to determine the SET's location.

In an exemplary handset-assisted, Network-initiated A-GPS location fixprocess, the LBA 240 may, in one embodiment, transmit a request to theSLP 210 for the location of a target SET 212. The SLP 210 may thentransmit a message to the SET 212 to commence the location determinationtransaction whereby the SET 212 provides a message in response to theSLP 210 including, for example, the Cell-ID of the serving base station252. The SLP 210 may then determine the coverage area of the cell andemploy this as an initial uncertainty area 254. The SLP 210 may thendetermine appropriate GPS assistance data utilizing the uncertainty area254 and may provide the same to the SET 212. The SET 212 would thenutilize the assistance data to lock onto a number of satellites 224 andreturn satellite measurements to the SLP 210. The SLP 210 may thendetermine the location of the SET 212 utilizing the satellitemeasurements provided by the SET 212 and provide the determined locationof the SET 212 to the LBA 240.

Table 1 below provides fields that may be sent from the SET 212 to theSLP 210 and utilized by the SLP 210 to determine the location of the SET212. The location of the SET 212 may be determined by the SLP 210 using,for example, code phase measurements (whole chips and fractional chips),Doppler measurements, and/or additional measurements provided by thenetwork, such as, but not limited to, Carrier to Noise ratio (C/N_(O)),a Multipath indicator, a Pseudorange RMS error, or other measurementsthat provide information regarding the quality of satellitemeasurements. Additional data provided by the SET 212 as discussed abovemay be, but is not limited to, the identification of the serving cell(Cell-ID). The SLP 210 may utilize the Cell-ID to determine appropriatecell information from a database. This cell information may include thelocation of the cell which can then be employed by the SLP 210 as aninitial location to calculate assistance data or may also be utilized asa seed location for an exemplary position calculation.

TABLE 1 Parameter Range Units Notes GPS TOW The GPS time of weekSatellite ID 0-63 The identifier of the satellite. TO convert to PRN,add 1. C/N_(o) 0-63 db-Hz SET's estimate of the carrier to noise ratio.Doppler +/1 6553.6 Hz Doppler shift measured by SET for a satellitesignal. Whole chips 0-1022 chips Whole value of the code phasemeasurement in units of 1 chip. Fractional 0 to <1 chips Fractionalvalue of the code phase chips measurement. Multipath Indicator of themultipath as indicator measured by the SET and is set to low, medium orhigh. Pseudorange 0 to 112 meters Measured RMS error in meters. RMSerror

In a Network-initiated scenario, once the LS (e.g., SLP) determines thelocation of a SET, the location may be provided to the requestingnetwork entity. If the LS is trusted by the recipient of the location,then the location may be considered to be valid even though the locationmay not be valid. The integrity of the location calculated by the LS isimportant as it may be utilized by emergency services operators, may beused to gain restricted access to location based services, etc. Thus, anunscrupulous user or intermediary who successfully spoofs or falsifiesone or more location measurements may fraudulently gain access to abroadcast restricted to a particular set of geographically locatedusers, may provide the authorities with an incorrect location to, e.g.,a tracked shipment, may disguise criminal activities by deceiving alaw-enforcement LBA, etc. The aim of the spoofer may thus be to convincean LS to provide a location that the spoofer desires by falsifyingmeasurement data such that the location provided by the LS iseffectively predetermined by the spoofer.

To spoof a location, a user may need the satellite ephemeris which isgenerally employed to determine the location of the satellites for agiven time. The user may determine the range to each satellite in viewof the desired location and use these as a basis for determiningpseudorange measurements. These measurements are generally converted topseudoranges by simulating a clock error and/or introducing other errorssuch as ionosphere, troposphere and other random errors.

FIG. 3 provides an example of an SET falsifying its location to the SLPof FIG. 2. With reference to FIG. 3, an LBA 240 may request the locationof a SET 300. In this example, the SET 300 may be positioned at acertain location 302 but is desirous to indicate that the user or SET300 is in another location 304. The spoofing SET 300 may utilizesatellite ephemeris to calculate GPS measurements and send thecalculated GPS measurements to the SLP 210 which may then employ a PCFto determine the location of the spoofing SET 300. The determinedlocation 304 of the SET 300 may then be provided to the LBA 240. Aspoofer may thus employ ephemeris to determine the location of thesatellites (and hence the predicted pseudorange measurements). Theephemeris may be from a request to the SLP 210 for assistance data ormay be provided from another source (e.g., the Internet, theInternational GNSS Service (IGS), etc.). One piece of informationrequired by the spoofing SET 300 may be the Cell-ID. From the Cell-ID,the SLP 210 may determine the coverage area of the cell, calculateappropriate assistance data, and the Cell-ID may be utilized as theinitial location estimate for the PCF. The Cell-ID may also, in oneembodiment, be employed for location assurance on the SLP 210 as will bediscussed below. If the spoofing SET 300 desires to spoof a location inthe current cell within, e.g., 10 to 20 km, of his present location,then the Cell-ID may be employed to request assistance data which isthen utilized to determine the location of the satellites in view andcalculate pseudoranges. These pseudoranges may then be manipulated tointroduce errors, converted to code phases, and sent to the SLP 210 tospoof a desired location. Falsifying locations outside the current cellmay, however, require the spoofing SET to know the Cell-ID for thedesired location via a database or other method.

Generally, the spoofing SET may require the ephemeris and/or ionospheremodel, the GPS time at which to calculate the location (normally thecurrent time), the desired location (WGS 84 latitude, longitude,altitude), and/or a Cell-ID in the vicinity of the desired location. Inone embodiment, when the LS is an SLP, messaging between the SLP and thespoofing SET is illustrated in FIG. 4. With reference to FIG. 4, an LBA410 may request the location of a SET 430 and send a Mobile LocationProtocol (MLP) Standard Location Immediate Request (SLIR) to an SLP 420(step 401). The SLP 420 may then send, at step 402, a SUPL INIT messageto the spoofing SET 430 via, e.g., a WAP gateway 422. The spoofing SET430 may then determine the Cell-ID in the vicinity of a desired locationat step 403. The Cell ID may then be provided to the SLP 420 soassistance data that the SET 430 receives is relevant to the desiredlocation. The Cell-ID may in one instance be provided by a cell database432. A cell database 432 may be, but is not limited to, an externalentity such as a database on the Internet or a local database or adatabase provided by the spoofer over time. The spoofing SET 430 may, instep 404, provide a SUPL POS INIT message to the SLP 420 with thespoofed cell and the requested assistance data. In step 405, the SLP 420may return a SUPL POS message with the required assistance data, and instep 406 the spoofing SET 430 may employ the assistance data todetermine the measurements to the satellites from the desired locationand sends the same in a SUPL POS message. The SLP 420 may then, in step407, provide a SUPL END message to the spoofing SET 430 to terminate thelocation transaction and return a falsified location to the LBA 410 in aStandard Location Immediate Answer (SLIA) message in step 408. Thisprocedure may generally enable a spoofing SET to simulate locationsanywhere on the Earth if the SET 430 has access to an adequate celldatabase 432. Alternatively, assistance data may be provided from asource separate to the SLP 420 (e.g., the Internet or another networksource); thus, in step 404, the SET 430 may indicate that assistancedata is unnecessary and may receive a SUPL POS message (step 405)without assistance data. The SET 430 may then employ its external sourceof assistance data as an input to spoofing the GPS measurements.

FIG. 5 is an illustration of a SET-initiated, SET-assisted process. Withreference to FIG. 5, a spoofing SET 530 may determine a Cell-ID for acell in the vicinity of a desired location at step 501 and send the sameto the SLP 520 with details of the capabilities of the SET 530 in a SUPLSTART message at step 502. The SLP 520 may provide a SUPL RESPONSEmessage with the positioning method to use in step 503. The SET 530 maythen send a SUPL POS INIT message to the SLP 520 with the requestedassistance data in step 504. The SLP 520 may then return a SUPL POSmessage with the required assistance data in step 505. The spoofing SET530 may utilize the assistance data to determine the applicablemeasurements from the satellites with respect to the desired locationand send the measurements in a SUPL POS message, in step 506, to the SLP520. The SLP 520 determines a location (the desired location of thespoofing SET 530) and may cache the determined location (for subsequentlocation requests). The SLP 520 may then send a SUPL END message to thespoofing SET 530, in step 507, with the location of the SET 530 toterminate the location transaction.

To calculate a desired location, the spoofing SET may determine thelocation of all of certain GPS satellites at the time of transmissionand determine the elevation of satellites relative to the desiredlocation while discarding any that are below the horizon. The spoofingSET may also determine the ionosphere delay between the desired locationand a satellite using, e.g., the Klobuchar ionosphere model and may addapplicable delays to the measurements. The spoofing SET may alsodetermine the troposphere delay between the desired location and asatellite using, e.g., the Hopfield troposphere model and add the delayto the measurements. Finally, the spoofing SET may apply a satelliteclock correction and group delay to the range which may ultimatelyresult in an LS determining a location for the SET within a meter of thedesired location. This type of spoofing, however, may be easily detectedby an LS as the receiver clock error provided by the spoofing SET wouldbe very small (e.g., less than 1*10⁻¹⁰ seconds), the residualsdetermined as part of the least squares process would be small, and/orthe uncertainty ellipse would be small (e.g., less than 1 meter ofuncertainty). A more sophisticated spoofer, however, may manipulate themeasurements by introducing random errors to each measurement and/ormanipulate all of the measurements by a fixed amount thereby simulatinga handset clock error. Further, a more sophisticated spoofer may alsosend a subset of the satellite measurements instead of the complete setof satellites in view. In one embodiment of the present subject matter,a spoofing SET may thus be employed to validate anti-spoofing protectionon an LS and may also be used as a verification tool to simulatelocation measurements from anywhere on the Earth.

By way of another embodiment, for a SET to falsify measurements, severalcalculations must be performed. First, the location of all of the GPSsatellites at the time of transmission of the signal should bedetermined. The time of transmission may provide the time that asatellite signal took to travel from the satellite to the receiver andhence the range. With knowledge of the time of receipt, it may be notedthat the satellite has moved from the location where it was when ittransmitted the signal and the time of transmission should be correctedthrough, in one embodiment, an iterative process whereby at eachiteration the range may be re-calculated based upon a respectivetransmission time until the range between one iteration and the nextchanges by a small amount. For example, a satellite range may be set tozero and the following steps performed until the range between oneiteration and the next changes by a small amount: (i) re-adjust thesatellite transmission time by the following relationship:satelliteTransmitTime=spoofedTime−(satellite range/speed of light); (ii)calculate the location of the satellite at the satellite transmit time;(iii) determine the range to the satellite by the followingrelationship: Range=distance between desired location and satellitelocation. Satellite locations may be, in one embodiment, determinedusing the navigation model data as specified in the GPS IS 200specification or another specifications for other GNSSs. Next, theelevation for each satellite relative to the desired location may bedetermined and any elevation below the horizon discarded. Once thelocation of the satellites are determined, then their respectiveelevation angle relative to the ground at the desired location may becalculated. A mask angle may also be applied to discard satellites thatare below a specific angle. Unhealthy satellites may be discardedutilizing health bits in the ephemeris. The remaining set of satellitesmay now include all possible healthy satellites in view of the desiredlocation. A spoofing SET may then discard a certain number of thesatellites to provide measurements for a configured number of satellitesor a random number of satellites (e.g., greater than the minimum tocalculate a location). As it is uncommon that a normal GPS receiver isable to make range measurements to all possible satellites in view, thismay be used by an LS to determine that a SET is spoofing; therefore, theSET may discard a subset of satellites to disguise the fact that it isindeed spoofing its location or respective measurement(s). In anotherembodiment of the present subject matter, a spoofing SET may thus beutilized to validate anti-spoofing protection on an exemplary LS and/orused as a verification tool to simulate location measurements.

In another embodiment, the following steps may then be performed foreach satellite: (i) determine the satellite clock correction (distancein meters) and group delay for each satellite for its time oftransmission and store the same; (ii) apply a Geometric range correctionto compensate for the rotation of the earth during the predicted time offlight; (iii) re-calculate the range to the satellite from the desiredlocation to the corrected location of the satellite; (iv) determine theionosphere delay for each satellite between the desired location and thesatellite using the Klobuchar ionosphere model and add the delay to themeasurement; (v) determine the troposphere delay for each satellitebetween the desired location and the satellite using the Hopfieldtroposphere model and add the delay to the measurement; (vi) apply aconfigurable random error to each measurement; (vii) apply a clock errorto each measurement; and (viii) apply the satellite clock correction andgroup delay to the range using the following relationship:satRange=calculatedRange−satClockCorrectionMeters. Of course, anexemplary spoofing SET according to any embodiment of the presentsubject matter may be utilized to validate anti-spoofing protection on arespective LS and/or may be used a verification tool to simulatelocation measurements.

Some protection may be present on an exemplary SLP which may restrictthe ability of a spoofing SET to falsify a location anywhere on Earthsuch as, but not limited to, location assurance and Cell-ID integritymethods. For example, in one embodiment, an exemplary SLP may determinethe distance between the location determined from a cell lookup and theGPS-calculated location. If the distance is larger than a predeterminedthreshold, then the SLP may deem that the measurements are invalid andmay not provide the spoofed location to the LBA. An exemplary andnon-limiting distance for location assurance protection may be 50 km orless. A spoofing SET may, however, invalidate certain methods oflocation assurance protection by having a comprehensive cell ID databaseso the desired location is within the vicinity of one of the cells inthe database. Additional integrity checking and location assurance mayalso be provided in additional embodiments of the present subjectmatter.

For example, another embodiment of the present subject matter mayinclude an aspect of integrity checking by using a location calculatedby alternate location technology methods. For example, the locationselected by an exemplary MLC (e.g., the location having the most preciselocation technology or smallest uncertainty) may be compared with orcrosschecked against other calculated locations to thereby improve theintegrity of a determined location and to assist in protecting againstfalsified locations. Generally, the location of a target SET may bedetermined by multiple location technologies of various accuracy levels.For example, the location of the SET may be determined utilizing Cell-IDfollowed by A-GPS. Of course, the process may involve any number ofother location methods in series or parallel such as, but not limitedto, Assisted Global Navigation Satellite System (A-GNSS), Observed TimeDifference of Arrival (OTDOA), Enhanced Observed Time Difference (EOTD),Enhanced Cell-ID (e-CID), Angle of Arrival (AOA), Time Difference ofArrival (TDOA), Power Difference of Arrival (PDOA), Power of Arrival(POA), Time of Arrival (TOA), Frequency Difference of Arrival (FDOA),Global Navigation Satellite System (GNSS), Radio FrequencyIdentification (RFID), Near field communications (NFC), hybridtechnologies, proximity location technologies, and combinations thereof.Thus, an embodiment of the present subject matter may check the selectedlocation of a target SET or device against any number or combinations ofthe other location(s) to determine whether or not they are consistent.Each of these respective locations may have an uncertainty at a givenconfidence, and the locations may be deemed to be consistent if theirboundaries are within a predefined threshold. Of course, additionalsatellite measurements may also be utilized as a source for detectinglocation spoofing, such as, but not limited to, GNSS signal strength,satellite identification codes, number of satellite signals received,time intervals, clock bias, code phases, Doppler shift, and combinationsthereof.

FIG. 6 is a schematic representation of one embodiment of the presentsubject matter. With reference to FIG. 6, a Cell-ID calculated location610 with an uncertainty circle 612 for an omnicell and a GPS calculatedlocation 620 with its uncertainty ellipse 622 are provided. Theselocations may be determined as consistent or valid as, for example, theGPS uncertainty ellipse 622 (or location 620) is within the uncertaintycircle 612 from the Cell-ID location 610.

FIG. 7 is a schematic representation of another embodiment of thepresent subject matter. With reference to FIG. 7, a Cell-ID calculatedlocation 710 with an uncertainty circle 712 and a GPS calculatedlocation 720 with its uncertainty ellipse 722 are provided where the GPScalculated location 720 does not lie within the boundary of the Cell-IDlocation and uncertainty circle 712. In this embodiment, if the distance730 between the boundaries (from the uncertainty at a predeterminedconfidence) of the uncertainty circle 712 and ellipse 722 is smallerthan a given threshold, then the locations may be deemed to beconsistent or valid. If, however, the distance 730 is greater than thethreshold, then the location 720 may be determined as invalid. If alocation is determined as invalid, the MLC may return an error, mark therespective location transaction as including a potentially spoofed orfalsified location, and/or remove the falsified measurement(s) anddetermine a location of the SET through any number or combinations ofother methods. Of course, the consistency threshold for the distancebetween the uncertainty boundaries may also be different for differentlocation technologies depending upon the reliability of the locationscalculated.

FIG. 8 is a schematic representation of a further embodiment of thepresent subject matter. With reference to FIG. 8, a Cell-ID calculatedlocation 810 and uncertainty circle 812 are provided along with a GPScalculated location 820 and uncertainty ellipse 822 and an RTT rangering 830. In this embodiment, the GPS location 820 and/or ellipse 822 isconsistent with all of the other location results and may thus bedetermined as a valid location.

FIG. 9 is a schematic representation of an additional embodiment of thepresent subject matter. With reference to FIG. 9, a Cell-ID calculatedlocation 910 and uncertainty circle 912 are provided with a GPScalculated location 920 and uncertainty ellipse 922 and an RTT rangering 930. In this embodiment, even if the GPS location 920 and/orellipse 922 is outside the Cell-ID location and uncertainty circle 912,the location 920 may still pass the threshold test for the Cell-IDlocation but fail the consistency check with the RTT range ring 930. Inthis case, the location may be determined as invalid, and the MLC mayreturn an error, mark the respective location transaction as including apotentially spoofed or falsified location, or remove the falsifiedmeasurement(s), and/or determine the location through any number orcombinations of other methods. Of course, the aforementioned embodimentsillustrated in FIGS. 6-9 may include location determinations using anynumber of location methods, such as, but not limited to, OTDOA, EOTD,e-CID, AOA, TDOA, PDOA, POA, TOA, FDOA, GNSS, RFID, NFC, hybridtechnologies, proximity location technologies, and combinations thereof,and such embodiments should not limit the scope of the claims appendedherewith.

In an alternative embodiment, Cell-ID integrity may be provided where anexemplary SLP may utilize network signaling to validate and/or check thereported Cell-ID. For example, when the SLP receives a Cell ID from theSET, the SLP may send a message through nodes in the respective networkto validate whether the SET is actually attached to that cell. The onlyway for a spoofing SET to avoid this protection is to utilize theCell-ID to which the spoofing SET is attached. Thus, if the spoofing SETdesires to falsify a location on the other side of the Earth from thatcell, assistance data must be retrieved from an external entity such asdescribed above as the SLP may provide assistance data specific to thesupplied Cell-ID. If an exemplary SLP has both Cell-ID integrity andlocation assurance, a spoofing SET is restricted to spoofing locationswithin the vicinity of that cell thereby providing location assuranceprotection to a respective server of 50 km or less. The LS may, in oneembodiment, include Cell-ID integrity by default. For example, an SMLCin a GERAN network or a SAS in a UTRAN network may provide Cell-IDsrather than the Cell-ID being provided by a SET. Thus, for thesenetworks, a spoofing SET may be restricted to falsifying a locationwithin the vicinity of the cell if location assurance according toembodiments of the present subject matter is enabled.

FIG. 10 is a block diagram of one embodiment of the present subjectmatter. With reference to FIG. 10, a method 1000 is provided fordetermining whether an estimated location of a wireless device includesone or more forged location measurements. The method may include at step1010 determining a first estimated location of the wireless device usinga first set of location measurements and at step 1020, determining asecond estimated location of the wireless device using a second set oflocation measurements. The first set and second set of locationmeasurements may be produced using a location technology such as, butnot limited to, Cell-ID, A-GNSS, OTDOA, EOTD, e-CID, AOA, TDOA, PDOA,POA, TOA, FDOA, GNSS, RFID, NFC, hybrid technologies, proximity locationtechnologies, and combinations thereof. In one embodiment, the secondset of location measurements may be produced using a location technologydifferent than the location technology used to produce the first set oflocation measurements. The first set of location measurements may beprovided by a database having information from a reference stationnetwork. Further, the first estimated location may be determined as afunction of coarse acquisition (“C/A”) code phase shift information,Doppler information or signals provided by a cellular network. Ofcourse, the first estimated location may be determined using locationmeasurements from signals received from a first set of satellites, andthe second estimated location may be determined using locationmeasurements from signals received from a second set of satellites. Thesecond set of satellites may be mutually exclusive or a subset of thefirst set of satellites.

At step 1030, the first estimated location may be compared to the secondestimated location, and at step 1040, one of the determined locationsidentified as having one or more forged location measurements if thecomparison between the first estimated location and second estimatedlocation is greater than a predetermined threshold. In one embodiment,the predetermined threshold may be a function of the uncertainty of thelocation technology utilized to produce the first and/or second set oflocation measurements. In another embodiment, step 1030 may includecomparing the first estimated location and the first estimatedlocation's uncertainty at a given confidence to the second estimatedlocation and the second estimated location's uncertainty at a givenconfidence. In an additional embodiment, the method 1000 may includedetermining a third estimated location of the wireless device fromsignals using a third set of location measurements, the third setexcluding one or more location measurements from the set of locationmeasurements having a forged measurement.

FIG. 11 is a block diagram of one embodiment of the present subjectmatter. With reference to FIG. 11, a method 1100 is provided fordetermining whether an estimated location of a wireless device includesone or more forged location measurements. The method 1100 may include atstep 1110 determining a first estimated location of the wireless devicefrom information or signals provided by a cellular network and at step1120 determining a second estimated location of the wireless device fromsignals received from a set of satellites. The first and secondestimated locations may then be compared at step 1130, and the secondestimated location identified as having one or more forged signals ifthe comparison between the first estimated location and second estimatedlocation is greater than a predetermined threshold at step 1140. In anadditional embodiment, step 1130 may include comparing the firstestimated location and the first estimated location's uncertainty at agiven confidence to the second estimated location and the secondestimated location's uncertainty at a given confidence.

It may be emphasized that the above-described embodiments, particularlyany “preferred” embodiments, are merely possible examples ofimplementations, merely set forth for a clear understanding of theprinciples of the disclosure. Many variations and modifications may bemade to the above-described embodiments of the disclosure withoutdeparting substantially from the spirit and principles of thedisclosure. All such modifications and variations are intended to beincluded herein within the scope of this disclosure and the presentdisclosure and protected by the following claims. Embodiments of thesubject matter and the functional operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Embodiments of the subject matterdescribed in this specification can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a tangible program carrier for execution by, orto control the operation of a data processing apparatus. The tangibleprogram carrier can be a propagated signal or a computer readablemedium. The propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal thatis generated to encode information for transmission to suitable receiverapparatus for execution by a computer. The computer readable medium canbe a machine-readable storage device, a machine-readable storagesubstrate, a memory device, a composition of matter affecting amachine-readable propagated signal, or a combination of one or more ofthem.

The term “data processing apparatus” encompasses all apparatus, devices,and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A computer program (also known as a program, software, softwareapplication, script, or code) may be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program does notnecessarily correspond to a file in a file system. A program can bestored in a portion of a file that holds other programs or data (e.g.,one or more scripts stored in a markup language document), in a singlefile dedicated to the program in question, or in multiple coordinatedfiles (e.g., files that store one or more modules, subprograms, orportions of code). A computer program may also be deployed to beexecuted on one computer or on multiple computers that are located atone site or distributed across multiple sites and interconnected by acommunication network.

The processes and logic flows described herein may be performed by oneor more programmable processors executing one or more computer programsto perform functions by operating on input data and generating output.The processes and logic flows can also be performed by, and apparatuscan also be implemented as, special purpose logic circuitry, e.g., anFPGA (field programmable gate array) or an ASIC (application specificintegrated circuit). Processors suitable for the execution of a computerprogram include, by way of example, both general and special purposemicroprocessors, and any one or more processors of any kind of digitalcomputer. Generally, a processor may receive instructions and data froma read only memory or a random access memory or both. The essentialelements of a computer are a processor for performing instructions andone or more memory devices for storing instructions and data. Generally,a computer may also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto optical disks, or optical disks.However, a computer need not have such devices. Moreover, a computer canbe embedded in another device, e.g., a mobile telephone, a personaldigital assistant (PDA), a mobile audio or video player, a game console,a GNSS receiver, to name just a few.

Computer readable media suitable for storing computer programinstructions and data include all forms of non volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto optical disks; andCD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry. Toprovide for interaction with a user, embodiments of the subject matterdescribed in this specification can be implemented on a computer havinga display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystaldisplay) monitor, for displaying information to the user and a keyboardand a pointing device, e.g., a mouse or a trackball, by which the usercan provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well; for example, input from theuser can be received in any form, including acoustic, speech, or tactileinput.

Embodiments of the subject matter described in this specification can beimplemented in a computing system that includes a back end component,e.g., as a data server, or that includes a middleware component, e.g.,an application server, or that includes a front end component, e.g., aclient computer having a graphical user interface or a Web browserthrough which a user can interact with an implementation of the subjectmatter described is this specification, or any combination of one ormore such back end, middleware, or front end components. The componentsof the system can be interconnected by any form or medium of digitaldata communication, e.g., a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), e.g., the Internet. The computing system caninclude clients and servers. A client and server are generally remotefrom each other and typically interact through a communication network.The relationship of client and server arises by virtue of computerprograms running on the respective computers and having a client-serverrelationship to each other.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this specification in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable sub-combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination. Similarly, whileoperations are depicted in the drawings in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results. Incertain circumstances, multitasking and parallel processing may beadvantageous. Moreover, the separation of various system components inthe embodiments described above should not be understood as requiringsuch separation in all embodiments, and it should be understood that thedescribed program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts.

As shown by the various configurations and embodiments illustrated inFIGS. 1-11, a method and system for location assurance of a mobiledevice location have been described.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

I claim:
 1. A method for determining whether an estimated location of awireless device includes one or more forged location measurements,comprising the steps of: (a) determining a first estimated location ofthe wireless device using a first set of location measurements; (b)determining a second estimated location of the wireless device using asecond set of location measurements; (c) comparing the first estimatedlocation to the second estimated location, wherein the comparingcomprises: comparing the first estimated location and the firstestimated location's uncertainty at a first confidence that defines afirst region to the second estimated location and the second estimatedlocation's uncertainty at a second confidence that defines a secondregion, wherein the distance between the first region and the secondregion is greater than zero; and (d) identifying one of the determinedlocations as having one or more forged location measurements if thedistance between the first region and the second region is greater thana predetermined threshold; and (e) identifying the determined locationsas valid if the distance between the first region and the second regionis less than the predetermined threshold.
 2. The method of claim 1wherein the first set and second set of location measurements areproduced using a location technology selected from the group consistingof: Cell-identification (Cell-ID), Assisted Global Navigation SatelliteSystem (A-GNSS), Observed Time Difference of Arrival (OTDOA), EnhancedObserved Time Difference (EOTD), Enhanced Cell-ID (e-CID), Angle ofArrival (AOA), Time Difference of Arrival (TDOA), Power Difference ofArrival (PDOA), Power of Arrival (POA), Time of Arrival (TOA), FrequencyDifference of Arrival (FDOA), Global Navigation Satellite System (GNSS),Radio Frequency Identification (RFID), Near field communications (NFC),hybrid technologies, proximity location technologies, and combinationsthereof.
 3. The method of claim 2 wherein the GNSS is selected from thegroup consisting of: a Global Positioning System (GPS), Galileo system,GLONASS system, Quasi-Zenith Satellite System (QZSS), Beidou satellitesystem, Compass satellite system, Indian Regional Navigational SatelliteSystem (IRNSS) and combinations thereof.
 4. The method of claim 1wherein the second set of location measurements is produced using alocation technology different than the location technology used toproduce the first set of location measurements.
 5. The method of claim 1wherein the first estimated location is determined using locationmeasurements from signals received from a first set of satellites. 6.The method of claim 5 wherein the second estimated location isdetermined using location measurements from signals received from asecond set of satellites.
 7. The method of claim 6 wherein the secondset of satellites is mutually exclusive of the first set of satellites.8. The method of claim 6 wherein the second set of satellites is asubset of the first set of satellites.
 9. The method of claim 1 whereinthe predetermined threshold is a function of the uncertainty of thelocation technology utilized to produce the first and second set oflocation measurements.
 10. The method of claim 1 wherein the first setof location measurements is provided by a database having informationfrom a reference station network.
 11. The method of claim 1 wherein thefirst estimated location is determined as a function of coarseacquisition (“C/A”) code phase shift information, Doppler information orsignals provided by a cellular network.
 12. The method of claim 1further comprising the step of determining a third estimated location ofthe wireless device from signals using a third set of locationmeasurements, the third set excluding one or more location measurementsfrom the set of location measurements having a forged measurement. 13.The method of claim 1 wherein the wireless device is selected from thegroup consisting of: cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.
 14. The method of claim1 further comprising the step of utilizing network signaling to validatea reported Cell identification.
 15. The method of claim 14 wherein thestep of identifying further comprises identifying one of the determinedlocations as having one or more forged location measurements if thecomparison between the first estimated location and second estimatedlocation is greater than the predetermined threshold or if the reportedCell identification is invalid.